In modern mobile telecommunications systems a mobile station may have a choice as to whether to operate with a public cellular system or with an autonomous system, such as a private system or a residential system. Typically it will be desirable to operate with a selected autonomous system, which may provide a more favorable rate structure than the public cellular system(s), or that may provide a desired service not offered by the public cellular system(s). A particular autonomous system may be a residential system that serves the user's home, or a system that serves the user's workplace.
One such modern cellular system is referred to as IS-136, which is described in IS-136.1, Rev. A, February 1996, and subsequent updated releases. This system employs Digital Control Channels (DCCHs) that enable a mobile station to gain access to the system. When a mobile station scans for and subsequently monitors a DCCH, it is said to be "camped" on that particular DCCH. Page messages and other information are received from the DCCH.
Defined in this document are Public Service Profiles (PSPs) and Private Operating Frequencies (POFS). Section 6.3.3 describes a Control Channel Reselection procedure, wherein the mobile station measures the signal strength of the serving DCCH, a non-public search (NPS) DCCH, POFs, and all viable neighbor list (NL) entries stored in the mobile station.
Section 6.3.21 defines the criteria for PSP and POF determination. As specified, an autonomous system is a microsystem of Network Type Private and/or Residential that shares frequencies with the cellular network in an operator's SID area. The number of authorized autonomous systems, and their geographic locations, are controlled by the cellular operator. However, there may be a large number of autonomous systems per SID area, and the specific frequencies used by any autonomous system may be dynamic. These factors make it impractical for the cellular network Base Station/Mobile Switching Center/Interworking functions or BMIs to include the DCCHs of autonomous systems as neighbor list entries. The normal reselection procedures based solely on neighbor list entries are therefore supplemented for mobile stations searching for autonomous systems.
A mobile station is specified to store two sets of frequencies for each autonomous system's Private System Identification (PSID) or Residential System Identification (RSID) that it retains in memory. The first set of frequencies correspond to control channels that have been assigned to the cellular network BMIs in the general vicinity of the autonomous system. These frequencies, along with their corresponding Digital Verification Color Code (DVCC), or Digital Color Code (DCC), and System Identification/System Operator Code/Mobile Country Code (SID/SOC/MCC) are referred to as the Public Service Profiles (PSPs) for the autonomous system. The second set of frequencies represent potential operating frequencies of the autonomous system, and are termed the Private operating Frequencies (POFs). A mobile station is defined to allow for the storage of a minimum of four PSPs and four POFs per autonomous system PSID or RSID. The procedure for a mobile station to initialize and update PSPs and POFs is described below.
Each time a mobile station camps on a DCCH, the frequency and DVCC of each stored DCCH PSP are compared to the frequency and DVCC of the current DCCH. If both the frequency and DVCC of any of the stored PSPs match the frequency and DVCC of its current DCCH, then a candidate autonomous system is considered as identified and the mobile station proceeds to examine the supplementary PSP information as follows.
If the SID/SOC/MCC associated with the PSP under consideration corresponds to the PSID/RSID of the candidate autonomous system, the mobile station declares a PSP match. Otherwise, the mobile station declares a PSP mismatch for the PSP under consideration.
Each time a mobile station tunes to the strongest or second strongest dedicated analog control channel (ACC) while performing an Initialization task (see IS-136.2, Section 2.6.1) or optionally an Idle task (see IS-136.2, Section 2.6.2), the frequency, SID and DCC of each stored ACC PSP are compared to the frequency, SID and DCC of this ACC. If both the frequency, SID and DCC of any of the stored PSPs match with the frequency, SID and DCC of the strongest or second strongest dedicated ACC, the mobile station declares a PSP match. Otherwise, the mobile station declares a PSP mismatch for the PSP under consideration.
When a PSP match is declared while on a DCCH, the mobile station adds the POFs of the associated autonomous system to the list of channels identified as requiring measurements (see Section 6.3.3.1). The mobile station then, after an appropriate delay as required for channel measurement purposes (see Section 6.3.3.3), declares a Priority System Condition (see Section 6.2.3) and uses the POFs as the list of reselection candidates. The mobile station also determines the MS-ACC-PWR, RSS-ACC-MIN, SS-SUFF and DELAY (see Section 6.3.3.4.2) for the POFs prior to invoking or while executing the Control Channel Reselection procedure specified in Section 6.3.3. When a PSP match is declared while on an Analog Control Channel (ACC), the mobile station may determine that a DCCH is the preferred service provider, and enter the Control Channel Scanning and Locking State (see Section 6.2.2), using the associated POFs as candidates.
A mobile station is to allow for manual initialization of PSPs and POFs, and is to also allow for automatic initialization of PSPs and POFs upon initial selection of an autonomous system as follows.
(A) Whenever a mobile station camps on a DCCH supporting a Private System Identification (PSID) or Residential System Identification (RSID) that matches a PSID/RSID stored in its memory (see Sections 8.3.4 and 8.3.5), and the Public bit of a Network Type indicator is set to zero, the mobile station updates the PSPs and POFs stored for the corresponding PSID/RSID.
(B) To update the PSPs, the mobile station stores the first four neighbor list entries received within a Neighbor Cell message (see Section 6.4.1.2.1.1) or a Neighbor Cell (Multi Hyperband) message (see Section 6.4.1.2.2.10), that have a CELLTYPE of NON-PREFERRED. The mobile station first examines the Neighbor Cell List (TDMA) information element in an attempt to find four neighbors having a CELLTYPE of NON-PREFERRED. If four neighbors are not found in the Neighbor Cell List (TDMA) information element, the mobile station proceeds to examine the Neighbor Cell List (Other Hyperband) and then the Neighbor Cell List (Analog) information elements for additional neighbors.
(C) To update the POFs, the mobile station stores the first four neighbor list entries received within the Neighbor Cell message (see Section 6.4.1.2.1.1) or the Neighbor Cell (Multi Hyperband) message (see Section 6.4.1.2.2.10), that have a CELLTYPE of PREFERRED or REGULAR. The mobile station only examines the Neighbor Cell List (TDMA) information element in an attempt to find four neighbors having a CELLTYPE of PREFERRED or REGULAR.
(D) Whenever the mobile station stores a new set of PSPs or POFs for a given autonomous system, it deletes the previous PSPs or POFs for that autonomous system.
A disadvantage that results from these procedures, as currently specified, arises for the case of a mobile station that begins a call when located in a public system where there is no autonomous system coverage, and then subsequently moves during the call to an area where there is coverage by an autonomous system. In conventional practice, when the call is terminated DCCH information is provided by the BMI upon release from an analog voice channel or a digital traffic channel. The mobile station uses this information to scan for the DCCH. When located, the mobile station camps on the DCCH, subsequently declares a PSP match, and then starts to measure the POF channels. After a delay, required for channel measurement purposes, the mobile station executes the channel reselection procedure to the POF channel. It can be appreciated that this procedure can cause a significant and user perceptible delay in the mobile station finally camping on the DCCH of the desired autonomous system.